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1807.02325 | Deviations for the Capacity of the Range of a Random Walk | We obtain estimates for large and moderate deviations for the capacity of the
range of a random walk on $\mathbb{Z}^d$, in dimension $d\ge 5$, both in the
upward and downward directions. The results are analogous to those we obtained
for the volume of the range in two companion papers [AS17, AS19].
Interestingly, the main steps of the strategy we developed for the latter apply
in this seemingly different setting, yet the details of the analysis are
different
| math.PR |
1807.02326 | Cause-Effect Deep Information Bottleneck For Systematically Missing
Covariates | Estimating the causal effects of an intervention from high-dimensional
observational data is difficult due to the presence of confounding. The task is
often complicated by the fact that we may have a systematic missingness in our
data at test time. Our approach uses the information bottleneck to perform a
low-dimensional compression of covariates by explicitly considering the
relevance of information. Based on the sufficiently reduced covariate, we
transfer the relevant information to cases where data is missing at test time,
allowing us to reliably and accurately estimate the effects of an intervention,
even where data is incomplete. Our results on causal inference benchmarks and a
real application for treating sepsis show that our method achieves state-of-the
art performance, without sacrificing interpretability.
| stat.ML cs.LG |
1807.02327 | Unconventional anomalous Hall effect from antiferromagnetic domain walls
of Nd2Ir2O7 thin films | Ferroic domain walls (DWs) create different symmetries and ordered states
compared with those in single-domain bulk materials. In particular, the DWs of
an antiferromagnet (AFM) with non-coplanar spin structure have a distinct
symmetry that cannot be realized in those of their ferromagnet counterparts. In
this paper, we show that an unconventional anomalous Hall effect (AHE) can
arise from the DWs of a non-coplanar AFM, Nd2Ir2O7. Bulk Nd2Ir2O7 has a cubic
symmetry; thus, its Hall signal should be zero without an applied magnetic
field. The DWs generated in this material break the two-fold rotational
symmetry, which allows for finite anomalous Hall conductivity. A strong f-d
exchange interaction between the Nd and Ir magnetic moments significantly
influences antiferromagnetic domain switching. Our epitaxial Nd2Ir2O7 thin film
showed a large enhancement of the AHE signal when the AFM domains switched,
indicating that the AHE is mainly due to DWs. Our study highlights the symmetry
broken interface of AFM materials as a new means of exploring topological
effects and their relevant applications.
| cond-mat.str-el |
1807.02328 | Seifert fibering operators in 3d $\mathcal{N}=2$ theories | We study 3d $\mathcal{N}=2$ supersymmetric gauge theories on closed oriented
Seifert manifold---circle bundles over an orbifold Riemann surface---, with a
gauge group G given by a product of simply-connected and/or unitary Lie groups.
Our main result is an exact formula for the supersymmetric partition function
on any Seifert manifold, generalizing previous results on lens spaces. We
explain how the result for an arbitrary Seifert geometry can be obtained by
combining simple building blocks, the "fibering operators." These operators are
half-BPS line defects, whose insertion along the $S^1$ fiber has the effect of
changing the topology of the Seifert fibration. We also point out that most
supersymmetric partition functions on Seifert manifolds admit a discrete
refinement, corresponding to the freedom in choosing a three-dimensional spin
structure. As a strong consistency check on our result, we show that the
Seifert partition functions match exactly across infrared dualities. The
duality relations are given by intricate (and seemingly new) mathematical
identities, which we tested numerically. Finally, we discuss in detail the
supersymmetric partition function on the lens space $L(p,q)_b$ with rational
squashing parameter $b^2 \in \mathbb{Q}$, comparing our formalism to previous
results, and explaining the relationship between the fibering operators and the
three-dimensional holomorphic blocks.
| hep-th |
1807.02329 | Scattering of an alkali atomic beam on anti-spin-relaxation-coatings | We performed scattering experiments using a rubidium (Rb) atomic beam on
paraffin films and measured the angular and velocity distributions of scattered
atoms. The paraffin films were prepared in various ways and characterized by
atomic force microscopy and X-ray diffraction. The films exhibited various
roughnesses and crystal structures. The paraffin films preserved the spin
polarization of the scattered atoms. The measured angular distributions of all
prepared films were consistent with Knudsen's cosine law. The velocity
distributions were well fitted by Maxwell's distribution, characterized by a
temperature much closer to the film temperature than to the atomic-beam
temperature. We therefore concluded that the Rb atoms were well thermalized
with the paraffin films via single scattering events.
| physics.atom-ph |
1807.02330 | On the Measure of Maximal Entropy for Finite Horizon Sinai Billiard Maps | The Sinai billiard map $T$ on the two-torus, i.e., the periodic Lorentz gas,
is a discontinuous map. Assuming finite horizon, we propose a definition $h_*$
for the topological entropy of $T$. We prove that $h_*$ is not smaller than the
value given by the variational principle, and that it is equal to the
definitions of Bowen using spanning or separating sets. Under a mild condition
of sparse recurrence to the singularities, we get more: First, using a transfer
operator acting on a space of anisotropic distributions, we construct an
invariant probability measure $\mu_*$ of maximal entropy for $T$ (i.e.,
$h_{\mu_*}(T)=h_*$), we show that $\mu_*$ has full support and is Bernoulli,
and we prove that $\mu_*$ is the unique measure of maximal entropy, and that it
is different from the smooth invariant measure except if all non grazing
periodic orbits have multiplier equal to $h_*$. Second, $h_*$ is equal to the
Bowen--Pesin--Pitskel topological entropy of the restriction of $T$ to a
non-compact domain of continuity. Last, applying results of Lima and Matheus,
as upgraded by Buzzi, the map $T$ has at least $C e^{nh_*}$ periodic points of
period $n$ for all large enough $n \in \mathbb{N}$.
| math.DS math-ph math.FA math.MP math.SP nlin.CD |
1807.02331 | Topologically protected superconducting ratchet effect generated by
spin-ice nanomagnets | We have designed, fabricated and tested a robust superconducting ratchet
device based on topologically frustrated spin-ice nanomagnets. The device is
made of a magnetic Co honeycomb array embedded in a superconducting Nb film.
This device is based on three simple mechanisms: i) the topology of the Co
honeycomb array frustrates in-plane magnetic configurations in the array
yielding a distribution of magnetic charges which can be ordered or disordered
with in-plane magnetic fields, following spin-ice rules, ii) the local vertex
magnetization, which consists of a magnetic half vortex with two charged
magnetic N\'eel walls, iii) the interaction between superconducting vortices
and the asymmetric potentials provided by the N\'eel walls. The combination of
these elements leads to a superconducting ratchet effect. Thus, superconducting
vortices driven by alternating forces and moving on magnetic half vortices
generate a unidirectional net vortex flow. This ratchet effect is independent
of the distribution of magnetic charges in the array.
| cond-mat.supr-con |
1807.02332 | Optimal efficiency of the Q-cycle mechanism around physiological
temperatures from an open quantum systems approach | The Q-cycle mechanism entering the electron and proton transport chain in
oxygenic photosynthesis is an example of how biological processes can be
efficiently investigated with elementary microscopic models. Here we address
the problem of energy transport across the cellular membrane from an open
quantum system theoretical perspective. We model the cytochrome $b_6f$ protein
complex under cyclic electron flow conditions starting from a simplified
kinetic model, which is hereby revisited in terms of a quantum master equation
formulation and spin-boson Hamiltonian treatment. We apply this model to
theoretically demonstrate an optimal thermodynamic efficiency of the Q-cycle
around ambient and physiologically relevant temperature conditions.
Furthermore, we determine the quantum yield of this complex biochemical process
after setting the electrochemical potentials to values well established in the
literature. The present work suggests that the theory of quantum open systems
can successfully push forward our theoretical understanding of complex
biological systems working close to the quantum/classical boundary.
| quant-ph cond-mat.mes-hall |
1807.02333 | Reflexivity of Rings via Nilpotent Elements | An ideal $I$ of a ring $R$ is called left N-reflexive if for any $a\in$
nil$(R)$, $b\in R$, being $aRb \subseteq I$ implies $bRa \subseteq I$ where
nil$(R)$ is the set of all nilpotent elements of $R$. The ring $R$ is called
left N-reflexive if the zero ideal is left N-reflexive. We study the properties
of left N-reflexive rings and related concepts. Since reflexive rings and
reduced rings are left N-reflexive, we investigate the sufficient conditions
for left N-reflexive rings to be reflexive and reduced. We first consider basic
extensions of left N-reflexive rings. For an ideal-symmetric ideal $I$ of a
ring $R$, $R/I$ is left N-reflexive. If an ideal $I$ of a ring $R$ is reduced
as a ring without identity and $R/I$ is left N-reflexive, then $R$ is left
N-reflexive. If $R$ is a quasi-Armendariz ring and the coefficients of any
nilpotent polynomial in $R[x]$ are nilpotent in $R$, it is proved that $R$ is
left N-reflexive if and only if $R[x]$ is left N-reflexive. We show that the
concept of N-reflexivity is weaker than that of reflexivity and stronger than
that of left N-right idempotent reflexivity and right idempotent reflexivity
which are introduced in Section 5.
| math.RA |
1807.02334 | Twin-field Quantum Key Distribution without Phase Post-Selection | Twin-field quantum key distribution (TF-QKD) protocol and its variants, e.g.
phase-matching (PM) QKD and TF-QKD based on sending or not sending, are highly
attractive since they are able to overcome the well-known rate-loss limit for
QKD protocols without repeater: $R=O(\eta)$ with $\eta$ standing for the
channel transmittance. However, all these protocols require active phase
randomization and post-selection that play an essential role together in their
security proof. Counterintuitively, we find that in TF-QKD, beating the
rate-loss limit is still possible even if phase randomization and
post-selection in the coding mode are both removed, which means our final
secure key rate $R=O(\sqrt{\eta})$. Furthermore, our protocol is more feasible
in practice and more promising according to its higher final key rate in the
valid distance. Our security proof counters collective attack and can also
counter coherent attack in asymptotical case
| quant-ph |
1807.02335 | Annihilators of simple integrable weight $\mathfrak{sl}(\infty)$-modules | Let $\mathfrak{g}=\mathfrak{sl}(\infty)$. We compute the annihilators of a
class of simple integrable weight $\mathfrak{g}$-modules with
finite-dimensional weight spaces. It is a claim of I. Dimitrov, that this class
exhausts all simple integrable weight $\mathfrak{g}$-modules with
finite-dimensional weight spaces. The main feature of interest is that
Dimitrov's class of modules contains non highest weight modules. Here we
provide another construction for these modules, which allows to apply results
of [PP18] to compute such annihilators.
| math.RT |
1807.02336 | Managing approximation errors in quantum programs | We address the problem of distributing approximation errors in large-scale
quantum programs. It has been known for some time that when compiling quantum
algorithms for a fault-tolerant architecture, some operations must be
approximated as they cannot be implemented with arbitrary accuracy by the
underlying gate set. This leads to approximation errors which often can be
grouped along subroutines that the given quantum algorithm is composed of.
Typically, choices can be made as to how to distribute approximation errors so
that the overall error is kept beneath a user- or application-defined
threshold. These choices impact the resource footprint of the fault-tolerant
implementation. We develop an automatic approximation error management module
to tackle the resulting optimization problems. The module is based on annealing
and can be integrated into any quantum software framework. Using the benchmark
of simulating an Ising model with transverse field, we provide numerical
results to quantify the benefits and trade-offs involved in our approach.
| quant-ph cs.ET |
1807.02337 | The homotopy types of $Sp(2)$-gauge groups over closed, simply-connected
four-manifolds | We determine the number of distinct fibre homotopy types for the gauge groups
of principal $Sp(2)$-bundles over a closed, simply-connected four-manifold.
| math.AT |
1807.02338 | A quasi-conservative dynamical low-rank algorithm for the Vlasov
equation | Numerical methods that approximate the solution of the Vlasov-Poisson
equation by a low-rank representation have been considered recently. These
methods can be extremely effective from a computational point of view, but
contrary to most Eulerian Vlasov solvers, they do not conserve mass and
momentum, neither globally nor in respecting the corresponding local
conservation laws. This can be a significant limitation for intermediate and
long time integration. In this paper we propose a numerical algorithm that
overcomes some of these difficulties and demonstrate its utility by presenting
numerical simulations.
| math.NA physics.comp-ph |
1807.02339 | Bipartite graphs and the structure of finite-dimensional semisimple
Leibniz algebras | Given a finite connected bipartite graph, finite-dimensional indecomposable
semisimple Leibniz algebras are constructed. Furthermore, any
finite-dimensional indecomposable semisimple Leibniz algebra admits a similar
construction.
| math.RA |
1807.02340 | Testing Untestable Neural Machine Translation: An Industrial Case | Neural Machine Translation (NMT) has been widely adopted recently due to its
advantages compared with the traditional Statistical Machine Translation (SMT).
However, an NMT system still often produces translation failures due to the
complexity of natural language and sophistication in designing neural networks.
While in-house black-box system testing based on reference translations (i.e.,
examples of valid translations) has been a common practice for NMT quality
assurance, an increasingly critical industrial practice, named in-vivo testing,
exposes unseen types or instances of translation failures when real users are
using a deployed industrial NMT system. To fill the gap of lacking test oracle
for in-vivo testing of an NMT system, in this paper, we propose a new approach
for automatically identifying translation failures, without requiring reference
translations for a translation task; our approach can directly serve as a test
oracle for in-vivo testing. Our approach focuses on properties of natural
language translation that can be checked systematically and uses information
from both the test inputs (i.e., the texts to be translated) and the test
outputs (i.e., the translations under inspection) of the NMT system. Our
evaluation conducted on real-world datasets shows that our approach can
effectively detect targeted property violations as translation failures. Our
experiences on deploying our approach in both production and development
environments of WeChat (a messenger app with over one billion monthly active
users) demonstrate high effectiveness of our approach along with high industry
impact.
| cs.CL cs.AI cs.SE |
1807.02341 | Arbitrary order finite volume well-balanced schemes for the Euler
equations with gravity | This work presents arbitrary high order well balanced finite volume schemes
for the Euler equations with a prescribed gravitational field. It is assumed
that the desired equilibrium solution is known, and we construct a scheme which
is exactly well balanced for that particular equilibrium. The scheme is based
on high order reconstructions of the fluctuations from equilibrium of density,
momentum and pressure, and on a well balanced integration of the source terms,
while no assumptions are needed on the numerical flux, beside consistency. This
technique allows to construct well balanced methods also for a class of moving
equilibria. Several numerical tests demonstrate the performance of the scheme
on different scenarios, from equilibrium solutions to non steady problems
involving shocks. The numerical tests are carried out with methods up to fifth
order in one dimension, and third order accuracy in 2D.
| math.NA |
1807.02342 | Invariant entanglement and generation of quantum correlations under
global dephasing | We investigate the dynamics of quantum entanglement and more general quantum
correlations quantified respectively via negativity and local quantum
uncertainty for two qubit systems undergoing Markovian collective dephasing.
Focusing on a two-parameter family of initial two-qubit density matrices, we
study the relation of the emergence of the curious phenomenon of time-invariant
entanglement and the dynamical behavior of local quantum uncertainty.
Developing an illustrative geometric approach, we demonstrate the existence of
distinct regions of quantum entanglement for the considered initial states and
identify the region that allows for completely frozen entanglement throughout
the dynamics, accompanied by generation of local quantum uncertainty.
Furthermore, we present a systematic analysis of different dynamical behaviors
of local quantum uncertainty such as its sudden change or smooth amplification,
in relation with the dynamics of entanglement.
| quant-ph |
1807.02343 | Controlled ordering of topological charges in an exciton-polariton chain | We demonstrate, experimentally and theoretically, controlled loading of an
exciton-polariton vortex chain into a 1D array of trapping potentials.
Switching between two types of vortex chains, with topological charges of the
same or alternating sign, is realised by means of appropriate shaping of an
incoherent pump beam that drives the system to the regime of bosonic
condensation. In analogy to spin chains, these vortex sequences realise either
a "ferromagnetic" or an "anti-ferromagnetic" order, whereby the role of spin is
played by the orbital angular momentum. The "ferromagnetic" ordering of
vortices is associated with the formation of a persistent chiral current. Our
results pave the way for controlled creation of nontrivial distributions of
orbital angular momentum and topological order in a periodic exciton-polariton
system.
| cond-mat.quant-gas |
1807.02344 | The Cryogenic Anticoincidence Detector for ATHENA X-IFU: Preliminary
test of AC-S9 towards the Demonstration Model | Our team is developing the Cryogenic Anticoincidence Detector (CryoAC) of the
ATHENA X-ray Integral Field Unit (X-IFU). It is a 4-pixels TES-based detector,
which will be placed less than 1 mm below the main TES array detector. We are
now producing the CryoAC Demonstration Model (DM): a single pixel prototype
able to probe the detector critical technologies, i.e. the operation at 50 mK
thermal bath, the threshold energy at 20 keV and the reproducibility of the
thermal conductance between the suspended absorber and the thermal bath. This
detector will be integrated and tested in our cryogenic setup at INAF/IAPS, and
then delivered to SRON for the integration in the X-IFU Focal Plane Assemby
(FPA) DM.
In this paper we report the status of the CryoAC DM development, showing the
main result obtained with the last developed prototype, namely AC-S9. This is a
DM-like sample, which we have preliminary integrated and tested before
performing the final etching process to suspend the silicon absorber. The
results are promising for the DM, since despite the limitations due to the
absence of the final etching (high thermal capacity, high thermal conductance,
partial TES surface coverage), we have been able to operate the detector with
TB = 50 mK and to detect 6 keV photons, thus having a low energy threshold
fully compatible with our requirement (20 keV).
| astro-ph.IM physics.ins-det |
1807.02345 | Incidence angles maximizing the Goos-Haenchen shift in seismic data
analysis | In the solid/liquid and liquid/solid scenarios, for the cases in which the P
and S reflected waves are represented by complex amplitudes, we give the closed
formulas for the Goos-Haenchen phase from which we can then determine the
lateral displacements. We compare the results of the analysis done by using the
Zoeppritz equations with the calculations which appear in Optics. We also
discuss under which circumstances the plane wave analysis is valid and what
happens for critical incidence where divergences appear. For the liquid/solid
interface, the incidence angles maximizing the lateral displacement are given
as solutions of a polynomial equation.
| physics.geo-ph |
1807.02346 | A sudden change of the global magnetic field of the active M dwarf AD
Leo revealed by full Stokes spectropolarimetric observations | In this paper we present an analysis of the first high-resolution full Stokes
vector spectropolarimetric observations of the active M dwarf AD Leo. Based on
observations collected in 2016 with the ESPaDOnS instrument at CFHT, we derived
the least-squares deconvolved Stokes profiles and detected linear polarisation
signatures in spectral lines. At the same time, we discovered that the circular
polarisation profiles corresponding to our data set are significantly weaker
compared to all archival spectra of AD Leo, which exhibited approximately
constant profiles over the timescale of at least 6 years until 2012. Magnetic
maps obtained using Zeeman Doppler imaging confirm the sudden change in the
surface magnetic field. Although the total magnetic field energy decreased by
about 20% between 2012 and 2016, the field component responsible for the
observed circular polarisation signatures corresponds to a stronger field
occupying a smaller fraction of the stellar surface in the more recent map.
These results represent the first evidence that active M dwarfs with
dipole-dominated axisymmetric field topologies can undergo a long-term global
magnetic variation.
| astro-ph.SR |
1807.02347 | Interplay of Polarization and Time-Reversal Symmetry Breaking in
Synchronously Pumped Ring Resonators | Optically induced breaking of symmetries plays an important role in nonlinear
photonics, with applications ranging from optical switching in integrated
photonic circuits to soliton generation in ring lasers. In this work we study
for the first time the interplay of two types of spontaneous symmetry breaking
that can occur simultaneously in optical ring resonators. Specifically we
investigate a ring resonator (e.g. a fiber loop resonator or whispering gallery
microresonator) that is synchronously pumped with short pulses of light. In
this system we numerically study the interplay and transition between regimes
of temporal symmetry breaking (in which pulses in the resonator either run
ahead or behind the seed pulses) and polarization symmetry breaking (in which
the resonator spontaneously generates elliptically polarized light out of
linearly polarized seed pulses). We find ranges of pump parameters for which
each symmetry breaking can be independently observed, but also a regime in
which a dynamical interplay takes place. Besides the fundamentally interesting
physics of the interplay of different types of symmetry breaking, our work
contributes to a better understanding of the nonlinear dynamics of optical ring
cavities which are of interest for future applications including all-optical
logic gates, synchronously pumped optical frequency comb generation, and
resonator-based sensor technologies.
| physics.optics |
1807.02348 | Data-driven causal path discovery without prior knowledge - a benchmark
study | Causal discovery broadens the inference possibilities, as correlation does
not inform about the relationship direction. The common approaches were
proposed for cases in which prior knowledge is desired, when the impact of a
treatment/intervention variable is discovered or to analyze time-related
dependencies. In some practical applications, more universal techniques are
needed and have already been presented. Therefore, the aim of the study was to
assess the accuracies in determining causal paths in a dataset without
considering the ground truth and the contextual information. This benchmark was
performed on the database with cause-effect pairs, using a framework consisting
of generalized correlations (GC), kernel regression gradients (GR) and absolute
residuals criteria (AR), along with causal additive modeling (CAM). The best
overall accuracy, 80%, was achieved for the (majority voting) combination of
GC, AR, and CAM, however, the most similar sensitivity and specificity values
were obtained for AR. Bootstrap simulation established the probability of
correct causal path determination (which pairs should remain indeterminate).
The mean accuracy was then improved to 83% for the selected subset of pairs.
The described approach can be used for preliminary dependence assessment, as an
initial step for commonly used causality assessment frameworks or for
comparison with prior assumptions.
| stat.AP |
1807.02349 | A generalized Holling type II model for the interaction between
dextral-sinistral snails and Pareas snakes | Pareatic snakes possess outstanding asymmetry in the mandibular tooth number,
which has probably been caused by its evolution to improve the feeding on the
predominant dextral snails. Gene mutation can generate chiral inversion on the
snail body. A sinistral snail population can thrive in this ecological context.
The interactions between dextral/sinistral snails and Pareas snakes are modeled
in this paper by using a new generalized functional response of Holling type
II. Distinct Pareas species show different bilateral asymmetry degrees. This
parameter plays an essential role in our model and determines the evolution of
the populations. Stability of the solutions is also analyzed for different
regimes in the space of parameters.
| q-bio.PE |
1807.02350 | A Variational Time Series Feature Extractor for Action Prediction | We propose a Variational Time Series Feature Extractor (VTSFE), inspired by
the VAE-DMP model of Chen et al., to be used for action recognition and
prediction. Our method is based on variational autoencoders. It improves
VAE-DMP in that it has a better noise inference model, a simpler transition
model constraining the acceleration in the trajectories of the latent space,
and a tighter lower bound for the variational inference. We apply the method
for classification and prediction of whole-body movements on a dataset with 7
tasks and 10 demonstrations per task, recorded with a wearable motion capture
suit. The comparison with VAE and VAE-DMP suggests the better performance of
our method for feature extraction. An open-source software implementation of
each method with TensorFlow is also provided. In addition, a more detailed
version of this work can be found in the indicated code repository. Although it
was meant to, the VTSFE hasn't been tested for action prediction, due to a lack
of time in the context of Maxime Chaveroche's Master thesis at INRIA.
| cs.LG stat.ML |
1807.02351 | Loosely coherent searches for medium scale coherence lengths | The search for continuous gravitational waves demands computationally
efficient algorithms that can handle highly non-linear parameter spaces.
Loosely coherent algorithms establish upper limits and detect signals by
analyzing families of templates as a single unit. We describe a new
computationally efficient loosely coherent search intended for all-sky searches
over medium scale coherence lengths (3-300 hours).
| astro-ph.IM gr-qc |
1807.02352 | Relaxation, chaos, and thermalization in a three-mode model of a BEC | We study the complex quantum dynamics of a system of many interacting atoms
in an elongated anharmonic trap. The system is initially in a Bose-Einstein
condensed state, well described by Thomas-Fermi profile in the elongated
direction and the ground state in the transverse directions. After a sudden
quench to a coherent superposition of the ground and lowest energy transverse
modes, quantum dynamics starts. We describe this process employing a three-mode
many-body model. The experimental realization of this system displays decaying
oscillations of the atomic density distribution. While a mean-field description
predicts perpetual oscillations of the atomic density distribution, our quantum
many-body model exhibits a decay of the oscillations for sufficiently strong
atomic interactions. We associate this decay with the fragmentation of the
condensate during the evolution. The decay and fragmentation are also linked
with the approach of the many-body model to the chaotic regime. The approach to
chaos lifts degeneracies and increases the complexity of the eigenstates,
enabling the relaxation to equilibrium and the onset of thermalization. We
verify that the damping time and quantum signatures of chaos show similar
dependences on the interaction strength and on the number of atoms.
| cond-mat.quant-gas cond-mat.stat-mech quant-ph |
1807.02353 | Loop space homology of a small category | In a 2009 paper, Dave Benson gave a description in purely algebraic terms of
the mod $p$ homology of $\Omega(BG^\wedge_p)$, when $G$ is a finite group,
$BG^\wedge_p$ is the $p$-completion of its classifying space, and
$\Omega(BG^\wedge_p)$ is the loop space of $BG^\wedge_p$. The main purpose of
this work is to shed new light on Benson's result by extending it to a more
general setting. As a special case, we show that if $\mathcal{C}$ is a small
category, $|\mathcal{C}|$ is the geometric realization of its nerve, $R$ is a
commutative ring, and $|\mathcal{C}|^+_R$ is a "plus construction" for
$|\mathcal{C}|$ in the sense of Quillen (taken with respect to $R$-homology),
then $H_*(\Omega(|\mathcal{C}|^+_R);R)$ can be described as the homology of a
chain complex of projective $R\mathcal{C}$-modules satisfying a certain list of
algebraic conditions that determine it uniquely up to chain homotopy. Benson's
theorem is now the case where $\mathcal{C}$ is the category of a finite group
$G$, $R=\mathbb{F}_p$ for some prime $p$, and $|\mathcal{C}|^+_R=BG^\wedge_p$.
| math.AT |
1807.02354 | The stepping stone model in a random environment and the effect of local
heterogneities on isolation by distance patterns | We study a one-dimensional spatial population model where the population
sizes at each site are chosen according to a translation invariant and ergodic
distribution and are uniformly bounded away from 0 and infinity. We suppose
that the frequencies of a particular genetic type in the colonies evolve
according to a system of interacting diffusions, following the stepping stone
model of Kimura. We show that, over large spatial and temporal scales, this
model behaves like the solution to a stochastic heat equation with
Wright-Fisher noise with constant coefficients. These coefficients are the
effective diffusion rate of genes within the population and the effective local
population density. We find that, in our model, the local heterogeneity leads
to a slower effective diffusion rate and a larger effective population density
than in a uniform population. Our proof relies on duality techniques, an
invariance principle for reversible random walks in a random environment and a
convergence result for a system of coalescing random walks in a random
environment.
| math.PR |
1807.02355 | Photonics in highly dispersive media: The exact modal expansion | We present exact modal expansions for photonic systems including highly
dispersive media. The formulas, based on a simple version of the Keldysh
theorem, are very general since both permeability and permittivity can be
dispersive, anisotropic, and even possibly non reciprocal. A simple dispersive
test case where both plasmonic and geometrical resonances strongly interact
exemplifies the numerical efficiency of our approach.
| physics.optics physics.comp-ph |
1807.02356 | Hybrid Monte Carlo methods for sampling probability measures on
submanifolds | Probability measures supported on submanifolds can be sampled by adding an
extra momentum variable to the state of the system, and discretizing the
associated Hamiltonian dynamics with some stochastic perturbation in the extra
variable. In order to avoid biases in the invariant probability measures
sampled by discretizations of these stochastically perturbed Hamiltonian
dynamics, a Metropolis rejection procedure can be considered. The so-obtained
scheme belongs to the class of generalized Hybrid Monte Carlo (GHMC)
algorithms. We show here how to generalize to GHMC a procedure suggested by
Goodman, Holmes-Cerfon and Zappa for Metropolis random walks on submanifolds,
where a reverse projection check is performed to enforce the reversibility of
the algorithm for large timesteps and hence avoid biases in the invariant
measure. We also provide a full mathematical analysis of such procedures, as
well as numerical experiments demonstrating the importance of the reverse
projection check on simple toy examples.
| math.NA cs.NA |
1807.02357 | Autoregressive Wild Bootstrap Inference for Nonparametric Trends | In this paper we propose an autoregressive wild bootstrap method to construct
confidence bands around a smooth deterministic trend. The bootstrap method is
easy to implement and does not require any adjustments in the presence of
missing data, which makes it particularly suitable for climatological
applications. We establish the asymptotic validity of the bootstrap method for
both pointwise and simultaneous confidence bands under general conditions,
allowing for general patterns of missing data, serial dependence and
heteroskedasticity. The finite sample properties of the method are studied in a
simulation study. We use the method to study the evolution of trends in daily
measurements of atmospheric ethane obtained from a weather station in the Swiss
Alps, where the method can easily deal with the many missing observations due
to adverse weather conditions.
| stat.ME econ.EM |
1807.02358 | Tight Typings and Split Bounds | Multi types---aka non-idempotent intersection types---have been used to
obtain quantitative bounds on higher-order programs, as pioneered by de
Carvalho. Notably, they bound at the same time the number of evaluation steps
and the size of the result. Recent results show that the number of steps can be
taken as a reasonable time complexity measure. At the same time, however, these
results suggest that multi types provide quite lax complexity bounds, because
the size of the result can be exponentially bigger than the number of steps.
Starting from this observation, we refine and generalise a technique
introduced by Bernadet & Graham-Lengrand to provide exact bounds for the
maximal strategy. Our typing judgements carry two counters, one measuring
evaluation lengths and the other measuring result sizes. In order to emphasise
the modularity of the approach, we provide exact bounds for four evaluation
strategies, both in the lambda-calculus (head, leftmost-outermost, and maximal
evaluation) and in the linear substitution calculus (linear head evaluation).
Our work aims at both capturing the results in the literature and extending
them with new outcomes. Concerning the literature, it unifies de Carvalho and
Bernadet & Graham-Lengrand via a uniform technique and a complexity-based
perspective. The two main novelties are exact split bounds for the leftmost
strategy---the only known strategy that evaluates terms to full normal forms
and provides a reasonable complexity measure---and the observation that the
computing device hidden behind multi types is the notion of substitution at a
distance, as implemented by the linear substitution calculus.
| cs.PL cs.LO |
1807.02359 | A Pixel Space Method for Testing Dipole Modulation in the CMB
Polarization | We introduce a pixel space method to detect dipole modulation or
hemispherical power asymmetry in the cosmic microwave background (CMB)
polarization. The method relies on the use of squared total polarized flux
whose ensemble average picks up a dipole due to the dipole modulation in the
CMB polarization. The method is useful since it can be applied easily to
partial sky. We define several statistics to characterize the amplitude of the
detected signal. By simulations we show that the method can be used to reliably
extract the signal at 2.7$\sigma$ level or higher in future CORE-like missions,
assuming that the signal is present in the CMB polarization at the level
detected by the Planck mission in the CMB temperature. An application of the
method to the 2018 Planck data does not detect a significant effect, when
taking into account the presence of correlated detector noise and residual
systematics in data. Using the FFP10 we find the presence of a very strong bias
which might be masking any real effect.
| astro-ph.CO |
1807.02360 | Operator Noncommutativity and Irreversibility in Quantum Chaos | We argue that two distinct probes of quantum chaos, i.e., the growth of
noncommutativity of two unequal-time operators and the degree of
irreversibility in a time-reversal test, are equivalent for initially localized
states. We confirm this for interacting nonintegrable many-body systems and a
quantum kicked rotor. Our results show that three-point out-of-time-ordered
correlators dominate the growth of the squared commutator for initially
localized states, in stark contrast to four-point out-of-time-ordered
correlators that have extensively been studied for thermal initial states.
| cond-mat.stat-mech quant-ph |
1807.02361 | The Influence of Differential Privacy on Short Term Electric Load
Forecasting | There has been a large number of contributions on privacy-preserving smart
metering with Differential Privacy, addressing questions from actual
enforcement at the smart meter to billing at the energy provider. However,
exploitation is mostly limited to application of cryptographic security means
between smart meters and energy providers. We illustrate along the use case of
privacy preserving load forecasting that Differential Privacy is indeed a
valuable addition that unlocks novel information flows for optimization. We
show that (i) there are large differences in utility along three selected
forecasting methods, (ii) energy providers can enjoy good utility especially
under the linear regression benchmark model, and (iii) households can
participate in privacy preserving load forecasting with an individual
re-identification risk < 60%, only 10% over random guessing.
| cs.CR |
1807.02362 | Squares and associative representations of two dimensional evolution
algebras | We associate an square to any two dimensional evolution algebra. This
geometric object is uniquely determined, does not depend on the basis and
describes the structure and the behaviour of the algebra. We determine the
identities of degrees at most four, as well as derivations and automorphisms.
We look at the group of automorphisms as an algebraic group, getting in this
form a new algebraic invariant. The study of associative representations of
evolution algebras is also started and we get faithful representations for most
two-dimensional evolution algebras. In some cases we prove that faithful
commutative and associative representations do not exist, giving raise to the
class of what could be termed as "exceptional" evolution algebras (in the sense
of not admitting a monomorphism to an associative algebra with deformed
product).
| math.RA |
1807.02363 | Schoenberg coefficients and curvature at the origin of continuous
isotropic positive definite kernels on spheres | We consider the class $\Psi_d$ of continuous functions $\psi \colon [0,\pi]
\to \mathbb{R}$, with $\psi(0)=1$ such that the associated isotropic kernel
$C(\xi,\eta)= \psi(\theta(\xi,\eta))$ ---with $\xi,\eta \in \mathbb{S}^d$ and
$\theta$ the geodesic distance--- is positive definite on the product of two
$d$-dimensional spheres $\mathbb{S}^d$. We face Problems 1 and 3 proposed in
the essay Gneiting (2013b). We have considered an extension that encompasses
the solution of Problem 1 solved in Fiedler (2013), regarding the expression of
the $d$-Schoenberg coefficients of members of $\Psi_d$ as combinations of
$1$-Schoenberg coefficients. We also give expressions for the computation of
Schoenberg coefficients of the exponential and Askey families for all even
dimensions through recurrence formula. Problem 3 regards the curvature at the
origin of members of $\Psi_d$ of local support. We have improved the current
bounds for determining this curvature, which is of applied interest at least
for $d=2$.
| math.ST math.FA stat.TH |
1807.02364 | Quantum dynamics of a microwave resonator strongly coupled to a tunnel
junction | We consider the coupling of a single mode microwave resonator to a tunnel
junction whose contacts are at thermal equilibrium. We derive the quantum
master equation describing the evolution of the resonator field in the strong
coupling regime, where the characteristic impedance of the resonator is larger
than the quantum of resistance. We first study the case of a
normal-insulator-normal junction and show that a dc driven single photon source
can be obtained. We then consider the case of a superconductor-insulator-normal
and superconductor-insulator-superconductor junction. There, we show that the
Lamb shift induced by the junction gives rise to a nonlinear spectrum of the
resonator even when the junction induced losses are negligible. We discuss the
resulting dynamics and consider possible applications including quantum Zeno
dynamics and the realization of a qubit.
| cond-mat.mes-hall quant-ph |
1807.02365 | On minimal edge version of doubly resolving sets of a graph | In this paper, we introduce the edge version of doubly resolving set of a
graph which is based on the edge distances of the graph. As a main result, we
computed the minimum cardinality $\psi_E$ of edge version of doubly resolving
sets of family of $n$-sunlet graph $S_n$ and prism graph $Y_n$.
| math.CO |
1807.02366 | Identifying rotation in SASI-dominated core-collapse supernovae with a
neutrino gyroscope | Measuring the rotation of core-collapse supernovae (SN) and of their
progenitor stars is extremely challenging. Here it is demonstrated that
neutrinos may potentially be employed as stellar gyroscopes, if phases of
activity by the standing accretion-shock instability (SASI) affect the neutrino
emission prior to the onset of the SN explosion. This is shown by comparing the
neutrino emission properties of self-consistent, three-dimensional (3D) SN
simulations of a 15 M_sun progenitor without rotation as well as slow and fast
rotation compatible with observational constraints. The explosion of the fast
rotating model gives rise to long-lasting, massive polar accretion downflows
with stochastic time-variability, detectable e.g. by the IceCube Neutrino
Observatory for any observer direction. While spectrograms of the neutrino
event rate of non-rotating SNe feature a well-known sharp peak due to SASI for
observers located in the proximity of the SASI plane, the corresponding
spectrograms of rotating models show activity over a wide range of frequencies,
most notably above 200 Hz for rapid rotation. In addition, the Fourier power
spectra of the event rate for rotating models exhibit a SASI peak with lower
power than in non-rotating models. The spectra for the rotating models also
show secondary peaks at higher frequencies with greater relative heights
compared to the main SASI peak than for non-rotating cases. These rotational
imprints will be detectable for SNe at 10 kpc or closer.
| astro-ph.HE hep-ph |
1807.02367 | Neutrino-nucleus reactions on $^{16}$O based on new shell-model
Hamiltonians | Neutrino-induced reactions on $^{16}$O are investigated by shell-model
calculaions with new shell-model Hamiltonians, which can describe well the
structure of $p$-shell and $p$-$sd$ shell nuclei. Distribution of the
spin-dipole strengths in $^{16}$O, which give major contributions to the
$\nu$-$^{16}$O reaction cross sections, is studied with the new Hamiltonians.
Muon-capture reaction rates on $^{16}$O are also studied to discuss the
quenching of the axial-vector coupling in nuclear medium. Charged-current and
neutral-current reaction cross sections are evaluated in various particle and
$\gamma$ emission channels as well as the total ones at neutrino energies up to
$E_{\nu}\approx$ 100 MeV. Branching ratios for the various channels are
obtained by the Hauser-Feshbach statistical model calculations, and partial
cross sections for single- and multi-particle emission channels are evaluated.
The cross sections updated are compared with previous continuum random phase
approximation (CRPA) calculations. Effects of multi-particle emission channels
on nucleosynthesis in core-collapse supernova (SN) explosions are investigated.
Inclusion of $\alpha$p emission channels is found to lead to an enhancement of
production yields of $^{11}$B and $^{11}$C through $^{16}$O ($\nu$, $\nu$'
$\alpha$p) $^{11}$B and $^{16}$O ($\nu$, e$^{-}$ $\alpha$p) $^{11}$C reactions,
respectively.
| nucl-th |
1807.02368 | Momentum-dependent spin selection rule in photoemission with glide
symmetry | We present a comprehensive theory on the spin- and angle-resolved
photoemission spectroscopy (SARPES) of materials with glide-mirror symmetry,
focusing on the role of glide symmetry on the spin selection rule. In the
glide-symmetric SARPES configuration, where the surface of a material, the
incoming light and the outgoing photoelectrons are invariant under a glide
reflection, the spin polarization of photoelectrons is determined by the glide
eigenvalue of the initial state, which makes SARPES a powerful tool for
studying topological phases protected by glide symmetry. We also show that, due
to the nonsymmorphic character of glide symmetry, the spin polarization of a
photoelectron whose momentum is in the second surface Brillouin zone is the
opposite of the spin polarization of a photoelectron which is ejected from the
same initial Bloch state but whose momentum is in the first zone. This momentum
dependence of spin selection rule clearly distinguishes glide symmetry from
mirror symmetry and is particularly important if the Bloch wavevector of the
initial state is close to the first surface Brillouin zone boundary. As a proof
of principle, we simulate the SARPES from the surface states of KHgSb (010) and
investigate how the spin selection rule imposed by the glide symmetry manifests
itself in a real material.
| cond-mat.mtrl-sci |
1807.02369 | The combinatorial invariance conjecture for parabolic Kazhdan-Lusztig
polynomials of lower intervals | The aim of this work is to prove a conjecture related to the Combinatorial
Invariance Conjecture of Kazhdan-Lusztig polynomials, in the parabolic setting,
for lower intervals in every arbitrary Coxeter group. This result improves and
generalizes, among other results, the main results of [Advances in Math. {202}
(2006), 555-601], [Trans. Amer. Math. Soc. {368} (2016), no. 7, 5247--5269].
| math.CO math.RT |
1807.02370 | Deep Back Projection for Sparse-View CT Reconstruction | Filtered back projection (FBP) is a classical method for image reconstruction
from sinogram CT data. FBP is computationally efficient but produces lower
quality reconstructions than more sophisticated iterative methods, particularly
when the number of views is lower than the number required by the Nyquist rate.
In this paper, we use a deep convolutional neural network (CNN) to produce
high-quality reconstructions directly from sinogram data. A primary novelty of
our approach is that we first back project each view separately to form a stack
of back projections and then feed this stack as input into the convolutional
neural network. These single-view back projections convert the encoding of
sinogram data into the appropriate spatial location, which can then be
leveraged by the spatial invariance of the CNN to learn the reconstruction
effectively. We demonstrate the benefit of our CNN based back projection on
simulated sparse-view CT data over classical FBP.
| eess.IV cs.CV |
1807.02371 | End-to-End Race Driving with Deep Reinforcement Learning | We present research using the latest reinforcement learning algorithm for
end-to-end driving without any mediated perception (object recognition, scene
understanding). The newly proposed reward and learning strategies lead together
to faster convergence and more robust driving using only RGB image from a
forward facing camera. An Asynchronous Actor Critic (A3C) framework is used to
learn the car control in a physically and graphically realistic rally game,
with the agents evolving simultaneously on tracks with a variety of road
structures (turns, hills), graphics (seasons, location) and physics (road
adherence). A thorough evaluation is conducted and generalization is proven on
unseen tracks and using legal speed limits. Open loop tests on real sequences
of images show some domain adaption capability of our method.
| cs.CV cs.RO |
1807.02372 | Emission of solar chromospheric and transition region features related
to the underlying magnetic field | The emission of the upper atmosphere of the Sun is closely related to
magnetic field concentrations at the solar surface.
It is well established that this relation between chromospheric emission and
magnetic field is nonlinear. Here we investigate systematically how this
relation, characterised by the exponent of a power-law fit, changes through the
atmosphere, from the upper photosphere through the temperature minimum region
and chromosphere to the transition region.
We used spectral maps from IRIS: MgII and its wings, CII, and SiIV together
with magnetograms and UV continuum images from SDO. We performed a power-law
fit for the relation between each pair of observables and determine the
power-law index (or exponent) for these.
While the correlation between emission and magnetic field drops monotonically
with temperature, the power-law index shows a hockey-stick-type variation: from
the upper photosphere to the temperature-minimum it drops sharply and then
increases through the chromosphere into the transition region. This is even
seen through the features of the MgII line, this is, from k1 to k2 and k3. It
is irrespective of spatial resolution or feature types on the Sun.
In accordance with the general picture of flux-flux relations from the
chromosphere to the corona, above the temperature minimum the sensitivity of
the emission to the plasma heating increases with temperature. Below the
temperature minimum a different mechanism has to govern the opposite trend of
the power-law index with temperature. We suggest four possibilities, in other
words, a geometric effect of expanding flux tubes filling the available
chromospheric volume, the height of formation of the emitted radiation, the
dependence on wavelength of the intensity-temperature relationship, and the
dependence of the heating of flux tubes on the magnetic flux density.
| astro-ph.SR |
1807.02373 | Near Optimal Exploration-Exploitation in Non-Communicating Markov
Decision Processes | While designing the state space of an MDP, it is common to include states
that are transient or not reachable by any policy (e.g., in mountain car, the
product space of speed and position contains configurations that are not
physically reachable). This leads to defining weakly-communicating or
multi-chain MDPs. In this paper, we introduce \tucrl, the first algorithm able
to perform efficient exploration-exploitation in any finite Markov Decision
Process (MDP) without requiring any form of prior knowledge. In particular, for
any MDP with $S^{\texttt{C}}$ communicating states, $A$ actions and
$\Gamma^{\texttt{C}} \leq S^{\texttt{C}}$ possible communicating next states,
we derive a $\widetilde{O}(D^{\texttt{C}} \sqrt{\Gamma^{\texttt{C}}
S^{\texttt{C}} AT})$ regret bound, where $D^{\texttt{C}}$ is the diameter
(i.e., the longest shortest path) of the communicating part of the MDP. This is
in contrast with optimistic algorithms (e.g., UCRL, Optimistic PSRL) that
suffer linear regret in weakly-communicating MDPs, as well as posterior
sampling or regularised algorithms (e.g., REGAL), which require prior knowledge
on the bias span of the optimal policy to bias the exploration to achieve
sub-linear regret. We also prove that in weakly-communicating MDPs, no
algorithm can ever achieve a logarithmic growth of the regret without first
suffering a linear regret for a number of steps that is exponential in the
parameters of the MDP. Finally, we report numerical simulations supporting our
theoretical findings and showing how TUCRL overcomes the limitations of the
state-of-the-art.
| cs.LG stat.ML |
1807.02374 | A Structured Prediction Approach for Label Ranking | We propose to solve a label ranking problem as a structured output regression
task. We adopt a least square surrogate loss approach that solves a supervised
learning problem in two steps: the regression step in a well-chosen feature
space and the pre-image step. We use specific feature maps/embeddings for
ranking data, which convert any ranking/permutation into a vector
representation. These embeddings are all well-tailored for our approach, either
by resulting in consistent estimators, or by solving trivially the pre-image
problem which is often the bottleneck in structured prediction. We also propose
their natural extension to the case of partial rankings and prove their
efficiency on real-world datasets.
| stat.ML cs.LG |
1807.02375 | D-modules in birational geometry | It is well known that numerical quantities arising from the theory of
D-modules are related to invariants of singularities in birational geometry.
This paper surveys a deeper relationship between the two areas, where the
numerical connections are enhanced to sheaf theoretic constructions facilitated
by the theory of mixed Hodge modules. The emphasis is placed on the recent
theory of Hodge ideals.
| math.AG |
1807.02376 | Higgs inflation | The properties of the recently discovered Higgs boson together with the
absence of new physics at collider experiments allows us to speculate about
consistently extending the Standard Model of particle physics all the way up to
the Planck scale. In this context, the Standard Model Higgs non-minimally
coupled to gravity could be responsible for the symmetry properties of the
Universe at large scales and for the generation of the primordial spectrum of
curvature perturbations seeding structure formation. We overview the
minimalistic Higgs inflation scenario, its predictions, open issues and
extensions and discuss its interplay with the possible metastability of the
Standard Model vacuum.
| hep-ph astro-ph.CO gr-qc hep-th |
1807.02377 | Stable finite energy global vortices and asymptotic freedom | This work deals with global vortices in the three-dimensional spacetime. We
study the case of a simple model with $U(1)$ symmetry and find a way to
describe stable, finite energy global vortices. The price we pay to stabilize
the solution is the presence of scale invariance, but we have found a way to
trade it with an electric charge in a medium with generalized permittivity,
which is further used to capture the basic feature of asymptotic freedom.
| hep-th hep-ph |
1807.02378 | Latest predictions from the EbyE NLO EKRT model | We present the latest results from the NLO pQCD + saturation + viscous
hydrodynamics (EbyE NLO EKRT) model. The parameters in the EKRT saturation
model are fixed by the charged hadron multiplicity in the 0-5 \% 2.76 TeV Pb+Pb
collisions. The $\sqrt{s}$, $A$ and centrality dependence of the initial
particle production follows then from the QCD dynamics of the model. This
allows us to predict the $\sqrt{s}$ and $A$ dependence of the particle
production. We show that our results are in an excellent agreement with the
low-$p_T$ data from 2.76 TeV and 5.02 TeV Pb+Pb collisions at the LHC as well
as with the data from the 200 GeV Au+Au collisions at RHIC. In particular, we
study the centrality dependences of hadronic multiplicities, flow coefficients,
and various flow correlations. Furthermore, the nuclear mass number dependence
of the initial particle production and hydrodynamic evolution can be tested in
the 5.44 TeV Xe+Xe collisions at the LHC. To this end, we show our predictions
for charged particle multiplicities, and in particular, show how the
deformations of the Xe nuclei reflect into the flow coefficients.
| nucl-th hep-ph |
1807.02379 | Congruence preserving functions in the residue class rings of
polynomials over finite fields | In this paper, as an analogue of the integer case, we define congruence
preserving functions over the residue class rings of polynomials over finite
fields. We establish a counting formula for such congruence preserving
functions, determine a necessary and sufficient condition under which all
congruence preserving functions are also polynomial functions, and characterize
such functions.
| math.NT |
1807.02380 | Gravitational waves from compact binaries in post-Newtonian accurate
hyperbolic orbits | We derive from first principles third post-Newtonian (3PN) accurate
Keplerian-type parametric solution to describe PN-accurate dynamics of
non-spinning compact binaries in hyperbolic orbits. Orbital elements and
functions of the parametric solution are obtained in terms of the conserved
orbital energy and angular momentum in both Arnowitt-Deser-Misner type and
modified harmonic coordinates. Elegant checks are provided that include a
modified analytic continuation prescription to obtain our independent
hyperbolic parametric solution from its eccentric version. A prescription to
model gravitational wave polarization states for hyperbolic compact binaries
experiencing 3.5PN-accurate orbital motion is presented that employs our
3PN-accurate parametric solution.
| gr-qc |
1807.02381 | Plasmons in realistic graphene/hexagonal boron nitride moir\'e patterns | Van der Waals heterostructures employing graphene and hexagonal boron nitride
(hBN) crystals have emerged as a promising platform for plasmonics thanks to
the tunability of their collective modes with carrier density and record values
for plasmonics figures of merit. In this Article we investigate theoretically
the role of moir\'e-pattern superlattices in nearly aligned graphene on hBN by
using continuum-model Hamiltonians derived from ab initio calculations. We
calculate the system's energy loss function for a variety of chemical potential
values that are accessible in gated devices. Our calculations reveal that the
electron-hole asymmetry of the moir\'e bands leads to a remarkable asymmetry of
the plasmon dispersion between positive and negative chemical potentials,
showcasing the intricate band structure and rich absorption spectrum across the
secondary Dirac point gap for the hole bands.
| cond-mat.mes-hall |
1807.02382 | Optical polarisation variability of radio loud narrow line Seyfert 1
galaxies. Search for long rotations of the polarisation plane | Narrow line Seyfert 1 galaxies (NLSy1s) constitute the AGN subclass
associated with systematically smaller black hole masses. A few radio loud ones
have been detected in MeV -- GeV energy bands by Fermi and evidence for the
presence of blazar-like jets has been accumulated. In this study we wish to
quantify the temporal behaviour of the optical polarisation, fraction and
angle, for a selected sample of radio loud NLSy1s. We also search for rotations
of the polarisation plane similar to those commonly observed in blazars. We
have conducted R-band optical polarisation monitoring of a sample of 10 RL
NLSy1s 5 of which have been previously detected by Fermi. The dataset includes
observations with the RoboPol, KANATA, Perkins and Steward polarimeters. In the
cases where evidences for long rotations of the polarisation plane are found,
we carry out numerical simulations to assess the probability that they are
caused by intrinsically evolving EVPAs instead of observational noise. Even our
moderately sampled sources show indications of variability, both in
polarisation fraction and angle. For the four best sampled objects in our
sample we find multiple periods of significant polarisation angle variability.
In the two best sampled cases, namely J1505+0326 and J0324+3410, we find
indications for three long rotations. We show that although noise can induce
the observed behaviour, it is much more likely that the apparent rotation is
caused by intrinsic evolution of the EVPA. To our knowledge this is the very
first detection of such events in this class of sources. In the case of the
largest dataset (J0324+3410) we find that the EVPA concentrates around a
direction which is at 49.3\degr to the 15-GHz radio jet implying a projected
magnetic field at an angle of 40.7\degr to that axis.
| astro-ph.GA astro-ph.HE |
1807.02383 | Natural Language Processing for Information Extraction | With rise of digital age, there is an explosion of information in the form of
news, articles, social media, and so on. Much of this data lies in unstructured
form and manually managing and effectively making use of it is tedious, boring
and labor intensive. This explosion of information and need for more
sophisticated and efficient information handling tools gives rise to
Information Extraction(IE) and Information Retrieval(IR) technology.
Information Extraction systems takes natural language text as input and
produces structured information specified by certain criteria, that is relevant
to a particular application. Various sub-tasks of IE such as Named Entity
Recognition, Coreference Resolution, Named Entity Linking, Relation Extraction,
Knowledge Base reasoning forms the building blocks of various high end Natural
Language Processing (NLP) tasks such as Machine Translation, Question-Answering
System, Natural Language Understanding, Text Summarization and Digital
Assistants like Siri, Cortana and Google Now. This paper introduces Information
Extraction technology, its various sub-tasks, highlights state-of-the-art
research in various IE subtasks, current challenges and future research
directions.
| cs.CL cs.AI |
1807.02384 | Rigidity of the Bonnet-Myers inequality for graphs with respect to
Ollivier Ricci curvature | We introduce the notion of Bonnet-Myers and Lichnerowicz sharpness in the
Ollivier Ricci curvature sense. Our main result is a classification of all
self-centered Bonnet-Myers sharp graphs (hypercubes, cocktail party graphs,
even-dimensional demi-cubes, Johnson graphs $J(2n,n)$, the Gosset graph and
suitable Cartesian products). We also present a purely combinatorial
reformulation of this result. We show that Bonnet-Myers sharpness implies
Lichnerowicz sharpness. We also relate Bonnet-Myers sharpness to an upper bound
of Bakry-\'Emery $\infty$-curvature, which motivates a generalconjecture about
Bakry-\'Emery $\infty$-curvature.
| math.CO math.DG |
1807.02385 | The corolla polynomial: a graph polynomial on half-edges | The study of Feynman rules is much facilitated by the two Symanzik
polynomials, homogeneous polynomials based on edge variables for a given
Feynman graph. We review here the role of a recently discovered third graph
polynomial based on half-edges which facilitates the transition from scalar to
gauge theory amplitudes: the corolla polynomial. We review in particular the
use of graph homology in the construction of this polynomial.
| hep-th |
1807.02386 | Photo Screen: Shaping Perceptions of Residential Communities | Engaging residential communities with each other and with management remains
a challenge. Housing providers deploy a variety of engagement strategies, some
of which are supported by digital technologies. Their individual success is
varied and integrated, multipronged approaches are seen to be more successful.
As part of those, it is important to address people's perceptions of community
and places, as well as any practical issues that they face. We present the
design and evaluation of Photo Screen, a situated, public photo taking and
viewing screen which was deployed in the context of a new flagship housing
estate as part of a range of community engagement measures. In a new context,
we confirm the high levels of engagement that can be achieved with this simple
mechanism. We propose that photo 'tagging' might offer a second-stage
engagement mechanism and enable meaningful dialogue between residents and
management. Finally, we discuss how this playful activity allowed residents to
positively shape the perception of their community.
| cs.HC |
1807.02387 | Common Fixed Point Theorems in Fuzzy Metric Space with Applications | In this paper, we introduce a new class of implicit function to prove common
fixed point theorems in fuzzy metric space. Moreover we define a new altering
distance in terms of integral and utilize the same to deduce integral type
contractive conditions. Secondly we present application of main results to the
system of functional equations. At the end we give an example in support of
results of the paper.
| math.FA |
1807.02388 | Quasitriangular coideal subalgebras of $U_q(\mathfrak{g})$ in terms of
generalized Satake diagrams | Let $\mathfrak{g}$ be a finite-dimensional semisimple complex Lie algebra and
$\theta$ an involutive automorphism of $\mathfrak{g}$. According to G. Letzter,
S. Kolb and M. Balagovi\'c the fixed-point subalgebra $\mathfrak{k} =
\mathfrak{g}^\theta$ has a quantum counterpart $B$, a coideal subalgebra of the
Drinfeld-Jimbo quantum group $U_q(\mathfrak{g})$ possessing a universal
K-matrix $\mathcal{K}$. The objects $\theta$, $\mathfrak{k}$, $B$ and
$\mathcal{K}$ can all be described in terms of Satake diagrams. In the present
work we extend this construction to generalized Satake diagrams, combinatorial
data first considered by A. Heck. A generalized Satake diagram naturally
defines a semisimple automorphism $\theta$ of $\mathfrak{g}$ restricting to the
standard Cartan subalgebra $\mathfrak{h}$ as an involution. It also defines a
subalgebra $\mathfrak{k}\subset \mathfrak{g}$ satisfying $\mathfrak{k} \cap
\mathfrak{h} = \mathfrak{h}^\theta$, but not necessarily a fixed-point
subalgebra. The subalgebra $\mathfrak{k}$ can be quantized to a coideal
subalgebra of $U_q(\mathfrak{g})$ endowed with a universal K-matrix in the
sense of Kolb and Balagovi\'c. We conjecture that all such coideal subalgebras
of $U_q(\mathfrak{g})$ arise from generalized Satake diagrams in this way.
| math.QA math.RT |
1807.02389 | Accelerated physical emulation of Bayesian inference in spiking neural
networks | The massively parallel nature of biological information processing plays an
important role for its superiority to human-engineered computing devices. In
particular, it may hold the key to overcoming the von Neumann bottleneck that
limits contemporary computer architectures. Physical-model neuromorphic devices
seek to replicate not only this inherent parallelism, but also aspects of its
microscopic dynamics in analog circuits emulating neurons and synapses.
However, these machines require network models that are not only adept at
solving particular tasks, but that can also cope with the inherent
imperfections of analog substrates. We present a spiking network model that
performs Bayesian inference through sampling on the BrainScaleS neuromorphic
platform, where we use it for generative and discriminative computations on
visual data. By illustrating its functionality on this platform, we implicitly
demonstrate its robustness to various substrate-specific distortive effects, as
well as its accelerated capability for computation. These results showcase the
advantages of brain-inspired physical computation and provide important
building blocks for large-scale neuromorphic applications.
| cs.NE cs.ET |
1807.02390 | On the identification of $k$-inductively pierced codes using toric
ideals | Neural codes are binary codes in $\{0,1\}^n$; here we focus on the ones which
represent the firing patterns of a type of neurons called place cells. There is
much interest in determining which neural codes can be realized by a collection
of convex sets. However, drawing representations of these convex sets,
particularly as the number of neurons in a code increases, can be very
difficult. Nevertheless, for a class of codes that are said to be
$k$-inductively pierced for $k=0,1,2$ there is an algorithm for drawing Euler
diagrams. Here we use the toric ideal of a code to show sufficient conditions
for a code to be 1- or 2-inductively pierced, so that we may use the existing
algorithm to draw realizations of such codes.
| q-bio.NC |
1807.02391 | Extracting Actionable Knowledge from Domestic Violence Discourses on
Social Media | Domestic Violence (DV) is considered as big social issue and there exists a
strong relationship between DV and health impacts of the public. Existing
research studies have focused on social media to track and analyse real world
events like emerging trends, natural disasters, user sentiment analysis,
political opinions, and health care. However there is less attention given on
social welfare issues like DV and its impact on public health. Recently, the
victims of DV turned to social media platforms to express their feelings in the
form of posts and seek the social and emotional support, for sympathetic
encouragement, to show compassion and empathy among public. But, it is
difficult to mine the actionable knowledge from large conversational datasets
from social media due to the characteristics of high dimensions, short, noisy,
huge volume, high velocity, and so on. Hence, this paper will propose a novel
framework to model and discover the various themes related to DV from the
public domain. The proposed framework would possibly provide unprecedentedly
valuable information to the public health researchers, national family health
organizations, government and public with data enrichment and consolidation to
improve the social welfare of the community. Thus provides actionable knowledge
by monitoring and analysing continuous and rich user generated content.
| cs.IR cs.CL cs.LG stat.ML |
1807.02392 | Scalaron the healer: removing the strong-coupling in the Higgs- and
Higgs-dilaton inflations | We show that introducing $R^2$-term makes the Higgs-inflation and
Higgs-dilaton inflation consistent models: the strong coupling energy scales in
scalar, gauge and gravity sectors all are lifted up to the Planck scale.
| hep-ph hep-th |
1807.02393 | Simultaneous T-dualization of type II pure spinor superstring | In this article we consider simultaneous T-dualization of type II superstring
action in pure spinor formulation. Simultaneous T-dualization means that we
make T-dualization at the same time along some subset of initial coordinates
marked by $x^a$. The only imposed assumption stems from the applicability of
the Buscher T-dualization procedure - background fields do not depend on
dualized directions $x^a$. In this way we obtain the full form of the T-dual
background fields and T-dual transformation laws. Because two chiral sectors
transform differently, there are two sets of vielbeins and gamma matrices
connected by the local Lorentz transformation. Its spinorial representation is
the same as in the constant background case. We also found the full expression
for T-dual dilaton field.
| hep-th |
1807.02394 | A model reduction method for multiscale elliptic PDEs with random
coefficients using an optimization approach | In this paper, we propose a model reduction method for solving multiscale
elliptic PDEs with random coefficients in the multiquery setting using an
optimization approach. The optimization approach enables us to construct a set
of localized multiscale data-driven stochastic basis functions that give
optimal approximation property of the solution operator. Our method consists of
the offline and online stages. In the offline stage, we construct the localized
multiscale data-driven stochastic basis functions by solving an optimization
problem. In the online stage, using our basis functions, we can efficiently
solve multiscale elliptic PDEs with random coefficients with relatively small
computational costs. Therefore, our method is very efficient in solving target
problems with many different force functions. The convergence analysis of the
proposed method is also presented and has been verified by the numerical
simulation.
| math.NA |
1807.02395 | Side-Jump Induced Spin-Orbit Interaction of Chiral Fluids from Kinetic
Theory | We apply the Wigner-function approach and chiral kinetic theory to
investigate the angular momentum and polarization of chiral fluids composed of
Weyl fermions with background electric/magnetic fields and vorticity. It is
found that the quantum corrections in Wigner functions give rise to nonzero
anti-symmetric components in the canonical energy-momentum tensors, which are
responsible for the spin-orbit interaction. In global equilibrium, conservation
of the canonical angular momentum reveals the cancellation between the orbital
component stemming from side jumps with nonzero vorticity and the spin
component in the presence of an axial chemical potential. We further analyze
the conservation laws near local equilibrium. It turns out that the canonical
angular momentum is no longer conserved even in the absence of background
fields due to the presence of a local torque coming from the spin-orbit
interaction involving temperature/chemical-potential gradients, which is
implicitly led by collisions.
| nucl-th cond-mat.mes-hall hep-th |
1807.02396 | The isotropic constant of random polytopes with vertices on convex
surfaces | For an isotropic convex body $K\subset\mathbb{R}^n$ we consider the isotropic
constant $L_{K_N}$ of the symmetric random polytope $K_N$ generated by $N$
independent random points which are distributed according to the cone
probability measure on the boundary of $K$. We show that with overwhelming
probability $L_{K_N}\leq C\sqrt{\log(2N/n)}$, where $C\in(0,\infty)$ is an
absolute constant. If $K$ is unconditional we argue that even $L_{K_N}\leq C$
with overwhelming probability. The proofs are based on concentration
inequalities for sums of sub-exponential or sub-Gaussian random variables,
respectively, and, in the unconditional case, on a new $\psi_2$-estimate for
linear functionals with respect to the cone measure in the spirit of Bobkov and
Nazarov, which might be of independent interest.
| math.MG math.FA math.PR |
1807.02397 | Quality Diversity Through Surprise | Quality diversity is a recent family of evolutionary search algorithms which
focus on finding several well-performing (quality) yet different (diversity)
solutions with the aim to maintain an appropriate balance between divergence
and convergence during search. While quality diversity has already delivered
promising results in complex problems, the capacity of divergent search
variants for quality diversity remains largely unexplored. Inspired by the
notion of surprise as an effective driver of divergent search and its
orthogonal nature to novelty this paper investigates the impact of the former
to quality diversity performance. For that purpose we introduce three new
quality diversity algorithms which employ surprise as a diversity measure,
either on its own or combined with novelty, and compare their performance
against novelty search with local competition, the state of the art quality
diversity algorithm. The algorithms are tested in a robot navigation task
across 60 highly deceptive mazes. Our findings suggest that allowing surprise
and novelty to operate synergistically for divergence and in combination with
local competition leads to quality diversity algorithms of significantly higher
efficiency, speed and robustness.
| cs.NE |
1807.02398 | Signatures of Solar Cycle 25 in Subsurface Zonal Flows | The pattern of migrating zonal flow bands associated with the solar cycle,
known as the torsional oscillation, has been monitored with continuous global
helioseismic observations by the Global Oscillations Network Group, together
with those made by the Michelson Doppler Imager onboard the Solar and
Heliosepheric Observatory and its successor the Helioseismic and Magnetic
Imager onboard the Solar Dynamics Observatory, since 1995, giving us nearly two
full solar cycles of observations. We report that the flows now show traces of
the mid-latitude acceleration that is expected to become the main
equatorward-moving branch of the zonal flow pattern for Cycle 25. Based on the
current position of this branch, we speculate that the onset of widespread
activity for Cycle 25 is unlikely to be earlier than the middle of 2019.
| astro-ph.SR |
1807.02399 | Quantum Dynamics of the Square-Lattice Heisenberg Model | Despite nearly a century of study of the $S=1/2$ Heisenberg model on the
square lattice, there is still disagreement on the nature of its high-energy
excitations. By tuning toward the Heisenberg model from the exactly soluble
Ising limit, we find that the strongly attractive magnon interactions of the
latter naturally account for a number of spectral features of the Heisenberg
model. This claim is backed up both numerically and analytically. Using the
density matrix renormalization group method, we obtain the dynamical structure
factor for a cylindrical geometry, allowing us to continuously connect both
limits. Remarkably, a semi-quantitative description of certain observed
features arises already at the lowest non-trivial order in perturbation theory
around the Ising limit. Moreover, our analysis uncovers that high-energy
magnons are localized on a single sublattice, which is related to the
entanglement properties of the ground state.
| cond-mat.str-el |
1807.02400 | Beyond Surveys: Analyzing Software Development Artifacts to Assess
Teaching Efforts | This Innovative Practice Full Paper presents an approach of using software
development artifacts to gauge student behavior and the effectiveness of
changes to curriculum design. There is an ongoing need to adapt university
courses to changing requirements and shifts in industry. As an educator it is
therefore vital to have access to methods, with which to ascertain the effects
of curriculum design changes. In this paper, we present our approach of
analyzing software repositories in order to gauge student behavior during
project work. We evaluate this approach in a case study of a university
undergraduate software development course teaching agile development
methodologies. Surveys revealed positive attitudes towards the course and the
change of employed development methodology from Scrum to Kanban. However,
surveys were not usable to ascertain the degree to which students had adapted
their workflows and whether they had done so in accordance with course goals.
Therefore, we analyzed students' software repository data, which represents
information that can be collected by educators to reveal insights into learning
successes and detailed student behavior. We analyze the software repositories
created during the last five courses, and evaluate differences in workflows
between Kanban and Scrum usage.
| cs.SE cs.CY |
1807.02401 | Learning a Representation Map for Robot Navigation using Deep
Variational Autoencoder | The aim of this work is to use Variational Autoencoder (VAE) to learn a
representation of an indoor environment that can be used for robot navigation.
We use images extracted from a video, in which a camera takes a tour around a
house, for training the VAE model with a 4 dimensional latent space. After the
model is trained, each real frame has a corresponding representation point on
manifold in the latent space, and each representation point has corresponding
reconstructed image. For the navigation problem, we map the starting image and
destination image to the latent space, then optimize a path on the learned
manifold connecting the two points, and finally map the path back through
decoder to a sequence of images. The ideal sequence of images should correspond
to a route that is spatially continuous - i.e. neighbor images in the route
should correspond to neighbor locations in physical space. Such a route could
be used for navigation with computer vision techniques, i.e. a robot could
follow the image sequence from starting location to destination in the
environment step by step. We implement this algorithm, but find in our
experimental results that the resulting route is not satisfactory. The route
consist of several discontinuous image frames along the ideal routes, so that
the route could not be followed by a robot with computer vision techniques in
practice. In our evaluation, we propose two reasons for our failure to
automatically find continuous routes: (1) The VAE tends to capture global
structures, but discard the details; (2) the Euclidean similarity metric used
for measuring continuity between house images is sub-optimal. For further work,
we propose: trying other generative models like VAE-GANs which may be better at
reconstructing the details to learn the representation map, and adjusting the
similarity metric in the path selecting algorithm.
| cs.RO cs.CV cs.LG |
1807.02402 | Spin-polarized localization in a magnetized chain | We investigate a simple tight-binding Hamiltonian to understand the stability
of spin-polarized transport of states with an arbitrary spin content in the
presence of disorder. The general spin state is made to pass through a linear
chain of magnetic atoms, and the localization lengths are computed. Depending
on the value of spin, the chain of magnetic atoms unravels a hidden transverse
dimensionality that can be exploited to engineer energy regimes where only a
selected spin state is allowed to retain large localization lengths. An
analysis is carried out to understand the roles played by the spin projections
in different energy regimes of the range of states. We introduce a new measure,
viz, a spin-resolved localization length for this purpose. We study
uncorrelated disorder in the potential profile offered by the magnetic
substrate or in the orientations of the magnetic moments concerning a given
direction in space. Our results show that the spin filtering effect is robust
against weak disorder and hence the proposed systems should be good candidates
for experimental realizations of spin-selective transport.
| cond-mat.dis-nn cond-mat.mes-hall |
1807.02403 | Global existence for the 3-D semilinear damped wave equations in the
scattering case | We study the global existence of solutions to semilinear damped wave
equations in the scattering case with derivative power-type nonlinearity on
(1+3) dimensional nontrapping asymptotically Euclidean manifolds. The main idea
is to exploit local energy estimate, together with local existence to convert
the parameter $\mu$ to small one.
| math.AP |
1807.02404 | Global solvability of chemotaxis-fluid systems with nonlinear diffusion
and matrix-valued sensitivities in three dimensions | In this work we extend a recent result to chemotaxis fluid systems which
include matrix-valued sensitivity functions
$S(x,n,c):\Omega\times[0,\infty)^2\to\mathbb{R}^{3\times3}$ in addition to the
porous medium type diffusion, which were discussed in the previous work.
Namely, we will consider the system \begin{align*} \left\{
\begin{array}{r@{\,}c@{\,}c@{\ }l@{\quad}l@{\quad}l@{\,}c}
n_{t}&+&u\cdot\!\nabla n&=\Delta n^m-\nabla\!\cdot(nS(x,n,c)\nabla c),\
&x\in\Omega,& t>0,\\ c_{t}&+&u\cdot\!\nabla c&=\Delta c-c+n,\ &x\in\Omega,&
t>0,\\ u_{t}&+&(u\cdot\nabla)u&=\Delta u+\nabla P+n\nabla\phi,\ &x\in\Omega,&
t>0,\\ &&\nabla\cdot u&=0,\ &x\in\Omega,& t>0, \end{array}\right. \end{align*}
in a bounded domain $\Omega\subset\mathbb{R}^3$ with smooth boundary. Assuming
that $m\geq1$, $\alpha\geq0$ satisfy $m+\alpha>\frac43$, that the matrix-valued
function $S(x,n,c):\Omega\times[0,\infty)^2\to\mathbb{R}^{3\times3}$ satisfies
$|S(x,n,c)|\leq\frac{S_0}{(1+n)^{\alpha}}$ for some $S_0>0$ and suitably
regular nonnegative initial data, we show that the corresponding
no-flux-Dirichlet boundary value problem emits at least one global very weak
solution. Upon comparison with results for the fluid-free system this condition
appears to be optimal. Moreover, imposing a stronger condition for the
exponents $m$ and $\alpha$, i.e. $m+2\alpha>\frac{5}{3}$, we will establish the
existence of at least one global weak solution in the standard sense.
| math.AP |
1807.02405 | Simple geometric approximations for global atmospheres on moderately
oblate planets | Certain geometric approximations such as the widely used traditional
shallow-atmosphere, spherical-geoid (TSA-SG) and the deep-atmosphere,
spherical-geoid (DA-SG) approximations boil down to the specification of a
spatial metric tensor. In order to eliminate the leading-order errors due to
the SG and TSA approximations, a sequence of three metric geometric
approximations of increasing accuracy at high altitudes is obtained.
Their metric tensors possess a simple, closed-form analytical expression. The
approximations capture to leading order the oblateness of the planet, the
widening of atmospheric columns with height, the horizontal and vertical
variations of gravity and the non-traditional part of the Coriolis force.
Furthermore, for the first two approximations, the horizontal metric is
conformal (proportional) to the spherical metric, which simplifies analytical
and numerical formulations of the equations of motion.
| physics.ao-ph astro-ph.EP |
1807.02406 | Multi-atomic Annealing Heuristic for Static Dial-a-ride Problem | Dial-a-ride problem (DARP) deals with the transportation of users between
pickup and drop-off locations associated with specified time windows. This
paper proposes a novel algorithm called multi-atomic annealing (MATA) to solve
static dial-a-ride problem. Two new local search operators (burn and reform), a
new construction heuristic and two request sequencing mechanisms (Sorted List
and Random List) are developed. Computational experiments conducted on various
standard DARP test instances prove that MATA is an expeditious meta-heuristic
in contrast to other existing methods. In all experiments, MATA demonstrates
the capability to obtain high quality solutions, faster convergence, and
quicker attainment of a first feasible solution. It is observed that MATA
attains a first feasible solution 29.8 to 65.1% faster, and obtains a final
solution that is 3.9 to 5.2% better, when compared to other algorithms within
60 sec.
| cs.AI |
1807.02407 | Defining work done on electromagnetic field | The problem of defining work done on electromagnetic field (EMF) via moving
charges does not have a ready solution, because the standard Hamiltonian of EMF
does not predict gauge-invariant energy changes. This limits applications of
statistical mechanics to EMF. We obtained a new, explicitly gauge-invariant
Hamiltonian for EMF that depends only on physical observables. This Hamiltonian
allows to define thermodynamic work done on EMF and to formulate the second law
for the considered situation. It also leads to a direct link between this law
and the electrodynamic arrow of time, i.e. choosing retarded, and not advanced
solutions of wave-equations. Measuring the thermodynamic work can give
information on whether the photon mass is small but non-zero.
| physics.class-ph cond-mat.stat-mech physics.optics |
1807.02408 | Excitation of copper vapor lasers by direct discharge of storage
capacitor via the high-speed photothyristors | The possibility of using an optocoupler "pulsed fiber laser - photo
thyristor" as a switch in excitation circuits of copper vapor lasers (CVL) is
investigated. It is shown that such switch has a nanosecond speed, is able to
pass monopolar or alternating current pulses through CVL with a power of up to
10 MW and a repetition rate of up to tens of kilohertz with an electric
efficiency of excitation circuit of more than 95%. A simple but very accurate
model of photo thyristor is proposed, which can be used in full-scale CVL
modeling programs.
| cond-mat.other |
1807.02409 | Sum rules for characters from character-preservation property of matrix
models | One of the main features of eigenvalue matrix models is that the averages of
characters are again characters, what can be considered as a far-going
generalization of the Fourier transform property of Gaussian exponential. This
is true for the standard Hermitian and unitary (trigonometric) matrix models
and for their various deformations, classical and quantum ones. Arising
explicit formulas for the partition functions are very efficient for practical
computer calculations. However, to handle them theoretically, one needs to tame
the remaining finite sums over representations of a given size, which turns
into an interesting conceptual problem. Already the semicircle distribution in
the large-$N$ limit implies interesting combinatorial sum rules for characters.
We describe also implications to $W$-representations, including a character
decomposition of cut-and-join operators, which unexpectedly involves only
single-hook diagrams and also requires non-trivial summation identities.
| hep-th |
1807.02410 | Two-species active transport along cylindrical biofilaments is limited
by emergent topological hindrance | Active motion of molecules along filamentous structures is a crucial feature
of cell biology and is often modeled with the paradigmatic asymmetric simple
exclusion process. Motivated by recent experimental studies that have addressed
the stepping behavior of kinesins on microtubules, we investigate a lattice gas
model for simultaneous transport of two species of active particles on a
cylinder. The species are distinguished by their different gaits: While the
first species moves straight ahead, the second follows a helical path. We show
that the collective properties of such systems critically differ from those of
one-species transport in a way that cannot be accounted for by standard models.
This is most evident in a jamming transition far below full occupation, as well
as in non-equilibrium pattern formation. The altered behavior arises because -
unlike the case in single-species transport - any given position may be
targeted by two particles from different directions at the same time. However,
a particle can leave a given position only in one direction. This simple change
in connectivity significantly amplifies the impact of steric interactions and
thus becomes a key determinant of mixed species transport. We computationally
characterize this type of hindrance and develop a comprehensive theory for
collective two-species transport along a cylinder. Our observations show high
robustness against model extensions that account for additional biomolecular
features and demonstrate that even small fractions of a second species can
significantly alter transport. This suggests that our analysis is also relevant
in a biological context.
| cond-mat.stat-mech nlin.CG physics.bio-ph |
1807.02411 | Improved bounds on the extremal function of hypergraphs | A fundamental problem in pattern avoidance is describing the asymptotic
behavior of the extremal function and its generalizations. We prove an
equivalence between the asymptotics of the graph extremal function for a class
of bipartite graphs and the asymptotics of the matrix extremal function. We use
the equivalence to prove several new bounds on the extremal functions of
graphs. We develop a new method to bound the extremal function of hypergraphs
in terms of the extremal function of their associated multidimensional
matrices, improving the bound of the extremal function of $d$-permutation
hypergraphs of length $k$ from $O(n^{d-1})$ to $2^{O(k)}n^{d-1}$.
| math.CO |
1807.02412 | Comments on Cooperative Density Estimation in Random Wireless Ad Hoc
Networks | In Onur et al. ["Cooperative density estimation in random wireless ad hoc
networks," IEEE Commun. Lett., vol. 16, no. 3, 269 pp. 331-333, Mar. 2012], two
novel density estimation (DE) approaches in wireless random networks were
introduced by Onur et al., which are carried out respectively in cooperative
and individual fashions. Both of them were derived via the maximum likelihood
(ML) method. However, an implicit but fatal error was made obtaining the
individual DE (I-DE) approach. This letter comments on Onur et al. and points
out the aforementioned error. By investigating the distance order statistics
(DOS) distributions in the random networks, the correct I-DE approach is
presented and discussed. Simulation results also show that the correct I-DE
outperforms the wrong one. More importantly, a new method that can obtain any
univariate or multivariate DOS distribution is demonstrated, which is expected
to be helpful for the study of the wireless communications and networking.
| cs.IT math.IT |
1807.02413 | Tunable bimodal explorations of space from memory-driven deterministic
dynamics | We present a wave-memory driven system that exhibits intermittent switching
between two propulsion modes in free space. The model is based on a point-like
particle emitting periodically cylindrical standing waves. Submitted to a force
related to the local wavefield gradient, the particle is propelled, while the
wave field stores positional information on the particle trajectory. For long
memory, the linear motion is unstable and we observe erratic switches between
two propulsive modes : linear motion and diffusive motion. We show that the
bimodal propulsion and the stochastic aspect of the dynamics at long time are
generated by a Shil'nikov chaos. The memory of the system controls the fraction
of time spent in each phase. The resulting bimodal dynamics shows analogies
with intermittent search strategies usually observed in living systems of much
higher complexity.
| cond-mat.stat-mech |
1807.02414 | Hydrodynamic Diffusion in Integrable Systems | We show that hydrodynamic diffusion is generically present in many-body
interacting integrable models. We extend the recently developed generalised
hydrodynamic (GHD) to include terms of Navier-Stokes type which lead to
positive entropy production and diffusive relaxation mechanisms. These terms
provide the subleading diffusive corrections to Euler-scale GHD for the
large-scale non-equilibrium dynamics of integrable systems, and arise due to
two-body scatterings among quasiparticles. We give exact expressions for the
diffusion coefficients. Our results apply to a large class of integrable
models, including quantum and classical, Galilean and relativistic field
theories, chains and gases in one dimension, such as the Lieb-Liniger model
describing cold atom gases and the Heisenberg quantum spin chain. We provide
numerical evaluations in the Heisenberg spin chain, both for the spin diffusion
constant, and for the diffusive effects during the melting of a small domain
wall of spins, finding excellent agreement with tDMRG numerical simulations.
| cond-mat.stat-mech cond-mat.quant-gas hep-th math-ph math.MP |
1807.02415 | Quantum shape effects and novel thermodynamic behaviors at nanoscale | Thermodynamic properties of confined systems depend on sizes of the
confinement domain due to quantum nature of particles. Here we show that shape
also enters as a control parameter on thermodynamic state functions. By
considering specially designed confinement domains, we separate the influences
of quantum size and shape effects from each other and demonstrate how shape
effects alone modify Helmholtz free energy, entropy and internal energy of a
confined system. We propose an overlapped quantum boundary layer method to
analytically predict quantum shape effects without even solving Schr\"odinger
equation or invoking any other mathematical tools. Thereby we reduce a
thermodynamic problem into a simple geometric one and reveal the profound link
between geometry and thermodynamics. We report also a torque due to quantum
shape effects. Furthermore, we introduce isoformal, shape preserving, process
which opens the possibility of a new generation of thermodynamic cycles
operating at nanoscale with unique features.
| cond-mat.mes-hall |
1807.02416 | A multidisciplinary task-based perspective for evaluating the impact of
AI autonomy and generality on the future of work | This paper presents a multidisciplinary task approach for assessing the
impact of artificial intelligence on the future of work. We provide definitions
of a task from two main perspectives: socio-economic and computational. We
propose to explore ways in which we can integrate or map these perspectives,
and link them with the skills or capabilities required by them, for humans and
AI systems. Finally, we argue that in order to understand the dynamics of
tasks, we have to explore the relevance of autonomy and generality of AI
systems for the automation or alteration of the workplace.
| cs.AI cs.CY |
1807.02417 | Defect mediated changes in structural, optical and photoluminescence
properties of Ni substituted CeO2 | Local and long range structure, optical and photoluminescence properties of
sol-gel synthesized Ce1-xNixO2 nanostructures have been studied. The crystal
structure, lattice strain and crystallite size have been analyzed. A decrease
in lattice parameter may be attributed to substitution of Ce with smaller Ni
ion. UV-Vis measurement is used for studying the effect of Ni substitution on
bandgap and disorder. The bandgap decreases with Ni substitution and disorder
increases. The PL spectra show five major peaks attributed to various defect
states. The PL emission decreases with Ni substitution owing to increase in
defects which acts as emission quenching centers. The lattice disorder and
defects have been studied using Raman spectroscopy. Raman measurement shows
that oxygen vacancies related defects are increasing with Ni substitution which
causes changes in optical and PL properties. Local structure measurements show
that Ni substitution leads to oxygen vacancies which does change host lattice
structure notably. Ce4+ to Ce3+ conversion increases with Ni substitution.
| cond-mat.mtrl-sci |
1807.02418 | A Semi-Lagrangian Spectral Method for the Vlasov-Poisson System based on
Fourier, Legendre and Hermite Polynomials | In this work, we apply a semi-Lagrangian spectral method for the
Vlasov-Poisson system, previously designed for periodic Fourier
discretizations, by implementing Legendre polynomials and Hermite functions in
the approximation of the distribution function with respect to the velocity
variable. We discuss second-order accurate-in-time schemes, obtained by
coupling spectral techniques in the space-velocity domain with a BDF
time-stepping scheme. The resulting method possesses good conservation
properties, which have been assessed by a series of numerical tests conducted
on the standard two-stream instability benchmark problem. In the Hermite case,
we also investigate the numerical behavior in dependence of a scaling parameter
in the Gaussian weight. Confirming previous results from the literature, our
experiments for different representative values of this parameter, indicate
that a proper choice may significantly impact on accuracy, thus suggesting that
suitable strategies should be developed to automatically update the parameter
during the time-advancing procedure.
| math.NA |
1807.02419 | On the nonlocal stabilization by starting control of the normal equation
generated from Helmholtz system | We consider the problem of stabilization to zero of semilinear normal
parabolic equations connected with the 3D Helmholtz system with periodic
boundary conditions and arbitrary initial datum. This problem was previously
studied in \cite{FSh16}. As it was recently revealed, the control function
suggested in that work contains a term impeding transference the stabilization
construction on the 3D Helmholtz system. The main concern of this article is to
prove that this term is not necessary for the stabilization result, and
therefore the control function can be changed by a proper way.
| math.OC |
1807.02420 | Reversed Active Learning based Atrous DenseNet for Pathological Image
Classification | Witnessed the development of deep learning in recent years, increasing number
of researches try to adopt deep learning model for medical image analysis.
However, the usage of deep learning networks for the pathological image
analysis encounters several challenges, e.g. high resolution (gigapixel) of
pathological images and lack of annotations of cancer areas. To address the
challenges, we proposed a complete framework for the pathological image
classification, which consists of a novel training strategy, namely reversed
active learning (RAL), and an advanced network, namely atrous DenseNet (ADN).
The proposed RAL can remove the mislabel patches in the training set. The
refined training set can then be used to train widely used deep learning
networks, e.g. VGG-16, ResNets, etc. A novel deep learning network, i.e. atrous
DenseNet (ADN), is also proposed for the classification of pathological images.
The proposed ADN achieves multi-scale feature extraction by integrating the
atrous convolutions to the Dense Block. The proposed RAL and ADN have been
evaluated on two pathological datasets, i.e. BACH and CCG. The experimental
results demonstrate the excellent performance of the proposed ADN + RAL
framework, i.e. the average patch-level ACAs of 94.10% and 92.05% on BACH and
CCG validation sets were achieved.
| cs.CV |
1807.02421 | Large-Scale Multiple Hypothesis Testing with the Normal-Beta Prime Prior | We revisit the problem of simultaneously testing the means of $n$ independent
normal observations under sparsity. We take a Bayesian approach to this problem
by introducing a scale-mixture prior known as the normal-beta prime (NBP)
prior. We first derive new concentration properties when the beta prime density
is employed for a scale parameter in Bayesian hierarchical models. To detect
signals in our data, we then propose a hypothesis test based on thresholding
the posterior shrinkage weight under the NBP prior. Taking the loss function to
be the expected number of misclassified tests, we show that our test procedure
asymptotically attains the optimal Bayes risk when the signal proportion $p$ is
known. When $p$ is unknown, we introduce an empirical Bayes variant of our test
which also asymptotically attains the Bayes Oracle risk in the entire range of
sparsity parameters $p \propto n^{-\epsilon}, \epsilon \in (0, 1)$. Finally, we
also consider restricted marginal maximum likelihood (REML) and hierarchical
Bayes approaches for estimating a key hyperparameter in the NBP prior and
examine multiple testing under these frameworks.
| stat.ME |
1807.02422 | A Semi-parametric Realized Joint Value-at-Risk and Expected Shortfall
Regression Framework | A new realized conditional autoregressive Value-at-Risk (VaR) framework is
proposed, through incorporating a measurement equation into the original
quantile regression model. The framework is further extended by employing
various Expected Shortfall (ES) components, to jointly estimate and forecast
VaR and ES. The measurement equation models the contemporaneous dependence
between the realized measure (i.e., Realized Variance and Realized Range) and
the latent conditional ES. An adaptive Bayesian Markov Chain Monte Carlo method
is employed for estimation and forecasting, the properties of which are
assessed and compared with maximum likelihood through a simulation study. In a
comprehensive forecasting study on 1% and 2.5 % quantile levels, the proposed
models are compared to a range of parametric, non-parametric and
semi-parametric models, based on 7 market indices and 7 individual assets.
One-day-ahead VaR and ES forecasting results favor the proposed models,
especially when incorporating the sub-sampled Realized Variance and the
sub-sampled Realized Range in the model.
| q-fin.RM q-fin.ST |
1807.02423 | Variations of the free implicative semilattice extension of a Hilbert
algebra | In [{\it On the free implicative semilattice extension of a Hilbert algebra}.
Mathematical Logic Quarterly 58, 3 (2012), 188--207], Celani and Jansana give
an explicit description of the free implicative semilattice extension of a
Hilbert algebra. In this paper we give an alternative path conducing to this
construction. Furthermore, following our procedure, we show that an adjunction
can be obtained between the algebraic categories of Hilbert algebras with
supremum and that of generalized Heyting algebras. Finally, in last section we
describe a functor from the algebraic category of Hilbert algebras to that of
generalized Heyting algebras, of possible independent interest.
| math.LO |
1807.02424 | Image Handling and Processing for Efficient Parking Space Detection and
Navigation Aid | This paper aims to develop a robust and flexible algorithm for vacant parking
space detections using the image processing capabilities of OpenCV. It removes
the need for independent sensors to detect a car and instead, uses real-time
images derived from various sources and servers to consider a group of slots
together. This greatly decreases the expenses required to design an efficient
parking system and increases the flexibility of the operation. This method
includes the use of a portable processing system with recognition algorithm and
has the option of extracting and importing images to the specified servers. The
results can be viewed on a custom website with the option to reserve the
particular empty slots and GPS navigations to the selected slots.
| eess.IV |